1. Field of the Invention
This invention relates in general to fasteners, and in particular to a machine screw that can be inserted into a mating threaded hole without rotating the screw.
2. Description of the Related Art
Most push-in fasteners are variations on the "pine tree" or "Christmas tree" structure, in which a shaft has a number of fins or ribs extending out from the shaft, either perpendicularly or at an angle toward the head of the fastener. The ribs are designed to deform as the fastener is inserted into the receiving hole. This deformation provides the frictional force required to hold the fastener in place. Unfortunately, the deformation also prevents the device from being removed easily without being damaged. These devices therefore are not normally used where the fastener is expected to be removed and reinserted.
Screws have been used for centuries to hold items together. U.S. Pat. No. 4,900,210, issued to Buchanan et al., on Feb. 13, 1990, discloses a fastener that can be pushed in, but must be unthreaded. The device uses thread segments that remain deformed against the inner surface of the mating receptacle. The receptacle has one turn of thread located at the mouth of the receptacle to engage the thread segments for unscrewing the fastener. This structure requires a special receptacle, and is not well adapted to use with conventional threaded holes, especially with the type of thread used for machine screws.
A need remained for a push-in fastener that fits the threaded hole designed to hold a machine screw. A need also remained for a fastener that could be inserted at an angle without binding. remained in the hole until removed by unscrewing. As always, a fastener that is less expensive and simple to construct was also desired.